Rotary fuel pump of the kind including cam-operated pistons



Nov. 9, 1965 ROTARY FUEL PUMP OF THE KIND INCLUDING CAM-OPERATED PISTONS Filed July 29, 1963 2 Sheets-Sheet 1 M. c. S..BARNARD ETAL 3,216,367 I Nov. 9, 1965 ROTARY FUEL PUMP OF THE KIND INCLUDING CAM-OPERATED PISTONS M. c. s. BARNARD ETAL 3,216,367

United States Patent 3,216,367 ROTARY FUEL PUMP OF THE KIND INCLUDING CAM-OPERATED PISTONS Mark C. S. Barnard and Anthony E. Martin, Solihull, England, assignors to The Rover Company Limited, Solihull, England Filed July 29, 1963, Ser. No. 298,163 Claims priority, application Great Britain, Aug. 4, 1962, 30,120/ 62 Claims. (Cl. 103162) The invention relates to a rotary fuel pump for supplying liquid fuel to a gas turbine engine, the pump being of the kind (hereinafter referred to as the kind described) comprising a housing containing a rotor, having a plurality of axially-extending bores therein, each bore containing a piston of which one end is engaged by a cam-plate inclined to the axis of rotation of the rotor, the bores having open ports in the end face of the rotor remote from the cam-plate and circumferentiallyspaced around the axis of the rotor so that, during rotation of the rotor in the housing, the ports pass suc cessively a fuel inlet and a fuel outlet in the form of circumferentially-spaced arcuate apertures, coaxially with the rotor and positioned in a stationary thrust face coacting with the said remote end face of the rotor.

In a gas turbine engine, the air-fuel ratio during starting and acceleration has to be kept substantially constant or varied in a predetermined manner. For example, in an aircraft engine, the fuel delivered by the pump should be varied automatically in response to a change of altitudc during acceleration of the engine up to full speed.

In pumps of the foregoing kind as known hitherto, the fuel delivery has been controlled by pivotally mounting the cam-plate so that its angle of inclination can be varied by a plunger engaging the inclined cam face and movable in response to a variable control signal. Due to the reaction of the inclined cam face a considerable force is required to be applied to the plunger to alter the angle of inclination and as the strength of the control signal is usually small, it has been necessary to provide servoassistance. An object of the present invention is to provide -a fuel pump in which the adjustment of the cam-plate is effected in another manner requiring considerably less force to make the adjustment and therefore avoiding the need for a servo-operated mechanism.

According to the invention, a liquid fuel pump of the kind described includes a cam-plate inclined at a fixed angle to the axis of rotation of the rotor, and rotatably mounted in the housing, whereby it is adjustable circumferentially to vary the angular positions of the beginning and end of the suction and discharge strokes of the pistons with respect to the arcuate inlet and outlet apertures and thereby to alter the effective arcuate length of the apertures, and means, operable in response to an operating condition of the engine, for eifecting the angular adjustment of the cam-plate.

The means for effecting angular adjustment of the camplate may comprise a piston responsive to change of fluid pressure in response to an operating condition of the engine, the piston being positioned within a chamber to which the said fluid pressure is applied and being connected to an angularly-movable arm, extending substantially radially from the axis of rotation of the cam plate. The said fluid pressure may conveniently be derived from the delivery from a compressor of a gas turbine engine to which the pump supplies liquid fuel.

Alternatively, where the said angular adjustment is to be effected in response to change of altitude, as in an aircraft engine, the means for angularly adjusting the camplate includes an evacuated capsule, arranged to produce a signal dependent upon an absolute pressure derived from atmospheric or an engine pressure. Conveniently, the capsule is arranged to move a rod pivotally connected to an angularly movable arm extending substantially radially from the axis of rotation of the cam-plate. The contraction of the capsule is preferably opposed by a spring, whereby as the altitude of the pump increases the expansion of the capsule is assisted by the spring. The diameter of the capsule and the rate of the spring are preferably made larger than is necessary so as to ensure that frictional forces in the actuating mechanism are overcome, thereby reducing the risk of a hysteresis effect due to friction in the mechanism and hence hysteresis in the air-fuel ratio control of the engine.

By way of example, two rotary fuel pumps for supplying liquid fuel to a gas turbine engine and including angularly-adjustable cam-plates in accordance with the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is an end view of the first pump and showing in section means for adjusting the cam-plate;

FIGURE 2 is a section through the pump on the line II-0II in FIGURE 1;

FIGURE 3 is a half section through the pump on the line III-0 in FIGURE 1;

FIGURE 4 is a section on the lines 1VIV in FIG- URES 2 and 3, and

FIGURE 5 is an end view, similar to FIGURE 1, of the second pump and shows in section alternative means for adjusting the cam-plate.

The pump shown in FIGURES 1 to 4 is of the kind described and illustrated in our U.S. patent application Ser. No. 149,746 which has matured into U.S. Patent No. 3,160,104 and briefly comprises a housing 1 in which is mounted a rotor 2 having three equi-angularly spaced bores therein extending parallel to its axis of rotation. Each bore contains a piston 3 of which one is shown in FIGURE 3. The left-hand end of each piston, as viewed in FIGURE 3, has a part-spherical recess therein in which is accommodated a ball 4, engaged similarly in a shoe 5 engaging a cam-plate 6, which has a cam-surface inclined to a tranverse plane perpendicular to the axis of rotation of the rotor. Each piston 3 is biased towardsthe cam-plate by a spring 7 acting between the piston and a plate 8 integral with the rotor shaft 9 and bolted to the rotor 2. The shaft 9 is provided with a coupling 20, whereby it can be driven by the engine (not shown). Except for angular adjustment of the cam-plate 6 in accordance with the present invention, the cam-plate 6 is stationary and therefore as the shaft 9 and the rotor 2 are rotated, the pistons 3 will be reciprocated in their bores by the combined action of the cam-plate 6 and the springs 7.

As more fully described in the aforesaid specification, the right-hand end of each bore in the rotor 2 communicates through passages such as 10 (see FIGURE 3) therein with a port in the right-hand face of the plate 8. The latter bears against a stationary thrust face on the lefthand end of a stationary bearing member 11 in which the shaft 9 rotates. The stationary thrust face includes two arcuate apertures 12 and 13 (see FIGURE 4), being respectively an inlet, communicating with the interior of the pump housing 1, and an outlet, communicating with a delivery passage 14 (see FIGURE 2). The stationary thrust face also includes a second outlet aperture 15 (see FIGURE 4) communicating with a second delivery passage (not shown). Fuel is admitted to the interior of the pump housing 1 from a reservoir (not shown) and as the rotor 2 is rotated the pistons 3 will pump fuel through the inlet aperture 12 and deliver it through the outlet apertures 13 and 15, as taught in the aforesaid specification. A by-pass passage 16 (see FIGURES 2 and 3) in the shaft 9 and communicating with the aperture 13 is normally closed by half-ball valves 17, constituting governors and carried on leaf springs 18 supported by the rotor 2. At certain rotational speeds, as taught in the aforesaid specification, one or both the half-ball valves 18 will open, thereby spilling fuel delivered through the aperture 13 to the interior of the pump housing 1.

As taught in the aforesaid specification, the angular adjustment of the cam-plate 6 effects variation in the angular positions of the beginning and end of the suction and delivery strokes of the pistons 3 relatively to the inlet 12 and the outlets 13 and 15. In accordance with a feature of the present invention, the cam-plate 6 in the pump shown in FIGURES 1 to 4 is mounted on a rotatable shaft 21 mounted in a bearing hole 22 at the left-hand end of the pump housing 1. The shaft 21 carries, externally of the housing 1, a radially-extending arm 23. The outer end of the arm 23 is carried in block 24, integral with a plunger 25 slidable in a cylindrical housing 26, mounted on the pump housing 1 (see FIGURE 1). The travel of the plunger 25 is limited by adjustable stops 27 and 28. The plunger 25 is biased in one direction by a spring 29 hearing between the back of the plunger and one end of the housing 26. The front of the plunger carries a cup-shaped seal 30 and defines with the adjacent end of the housing 26 a chamber 31 to which a fluid under pressure is applied through a port 32. The port 32 may be connected to any variable control fluid but is conveniently connected to the delivery duct of a compressor of a gas turbine engine supplied with fuel by the fuel pump. Thus as the compressor delivery pressure increases, the plunger 25 will be moved against the bias of the spring 29 and the cam-plate will be corresspondingly angularly adjusted, to vary the effective length of the outlet 13 thereby to effect a correcting change in the fuel flow to the engine. On decrease of compressor delivery pressure the spring 29 will return the plunger 25 thereby re-adjusting the cam-plate 6.

The pump described with reference to FIGURES 1 to 4 may be modified by using the delivery from the outlet 15 to apply a modifying pressure to the chamber 31; instead of using compressor delivery pressure and leading the delivery from the outlet 15 to the engine, Which would then receive only the fuel delivered by the arcuate outlet aperture 13. The modifying pressure is only applied to the chamber 31 at rotational speeds below that at which a low-speed governor (not shown) will open, to spill the delivery from the outlet 15 to the pump inlet. The effect of the modifying pressure is to increase the effective arcuate length of the arcuate outlet aperture 13, thereby to increase fuel flow on starting and initial acceleration, as is usually necessary.

The second pump shown in FIGURE is particularly intended for use with an aircraft gas turbine engine and is similar in construction to that shown in FIGURES 1 to 4 except for the manner in which the cam-plate 6 is angularly adjusted. As in the first pump, the cam-plate shaft 21 carries a radial arm 35. The latter is connected at its outer end to a rod 36, which is attached to an endplate 37 of an evacuated capsule in the form of a bellows 38. The opposite end-plate 39 of the bellows is anchored by a rod 40 to a fixed casing 41 mounted on the pump housing 1. A helical spring 42 positioned concentrically around the bellows 38 acts to bias the two end-plates 37 and 39 apart. On increase of altitude, the bellows 38 expands due to the fall in ambient pressure, the spring 42 assisting the expansion. The arm 35 is therefore turned through an angle depending upon the fall in ambient pressure and angular adjustment of the cam-plate 6 is thereby effected. On decrease of altitude the bellows 38 contracts as a result of the increase in ambient pressure and the spring 42 is compressed. The arm 35 is therefore turned in the opposite direction, thereby effecting re-adjustment of the cam-plate 6. The diameter of the bellows 38 and the rate of the spring 42 are preferably made larger than is necessary so as to ensure that frictional forces in the actuating mechanism are overcome, thereby reducing the risk of a hysteresis effect due to friction in the mechanism and hence hysteresis in the air-fuel ratio control of the engine. The casing 41 has a cover plate; but this has not been shown.

Although only compressor delivery pressure and atmospheric pressure have been used in the foregoing examples to control the positions of the cam-plate 6 another variable operating condition alfecting the engine may be used instead.

Although in the foregoing examples the pumps described are of the kind having two outlet apertures 13 and 15 as taught by US. patent application Ser. No. 149,746 which has matured into US. Patent No. 3,160,- 104 the angularly-adjustable cam-plate in accordance with the invention may be applied to a rotary piston pump having more than two outlet apertures or of the kind described in our US. Patent No. 3,085,619 in which there is only one arcuate outlet aperture. Instead of the fixed cam-plate of the latter specification the cam-plate is rotatably-mounted as in the pump illustrated in FIGURES l to 4 and is angularly-adjustable by fluid pressure or by variation of atmospheric pressure as described herein. The effect of turning the cam-plate through an angle from the normal position, in which each piston is in its top dead centre position when it is registering with the thrust face between the arcuate outlet and inlet apertures, is that each piston will be in its top dead centre position when it is registering with an intermediate position in the length of the outlet or suction aperture and thus th effective arcuate length of the outlet aperture will be decreased.

It has been found that the force required to be applied to the operating arm in order to provide sufiicient torque to turn the cam-plate is considerably less than that required to tip a pivotally-mounted cam-plate, as used hitherto, and that as a result no servo-mechanism is required. Thus the pump according to this invention is more simple and cheaper to produce than the known pump referred to herein.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. A liquid fuel pump comprising a housing, a rotor mounted within said housing and having a pair of opposed end faces and a plurality of bores therein extending be-,

tween said end faces; a piston in each bore; a spring in each bore operable to bias the respective piston towards a position in which it extends from one of said end faces; a cam-plate coaxial with, but inclined to, the axis of rotation of said rotor and positioned adjacent said one end face of said rotor, said cam-plate engaging said pistons and effecting their reciprocation in said bores as said rotor is rotated, the other of said end faces of said rotor having therein a plurality of ports communicating one with each said bore; a stationary thrust face in said housing coacting with said other end face of the rotor and having therein arcuate inlet and outlet apertures coaxial with the axis of said rotor, a bearing mounting for said cam-plate, whereby it is adjustable circumferentially to vary the angular positions of the beginning and end of the suction and discharge strokes of said pistons with respect to said arcuate inlet and outlet apertures and thereby to alter the effective arcuate length of said apertures, and means, operable to effect the angular adjustment of said cam-plate in response to change of altitude at which the pump is operated, said cam-plate adjustingmeans including an evacuated capsule, arranged to produce a signal dependent upon an absolute pressure derived from atmospheric pressure.

2. A pump as claimed in claim 1 in which said camplate adjusting-means also includes a rod operatively connected to said capsule, an angularly-movable arm, extending substantially radially from said cam-plate and pivotally connected at the end thereof remote from said cam-plate to said rod.

3. A pump as claimed in claim 2 in which said camplate adjusting-means also includes a spring arranged to oppose the contraction of said capsule, whereby as the altitude of the pump increases, the expansion of said capsule is assisted by said spring.

4. A pump as claimed in claim 3 in which the diameter of said capsule and the rate of said spring are made larger than is necessary, thereby to ensure that frictional forces in said cam-plate adjusting-means are overcome.

5. A liquid fuel pump comprising a housing, a rotor mounted within said housing and having a pair of op posed end faces and a plurality of bores therein extending between said end faces; a piston in each bore; a spring in each bore operable to bias the respective piston towards a position in which it extends from one of said end faces; a cam-plate coaxial with, but inclined to, the axis of rotation of said rotor and positioned adjacent said one end face of said rotor, said cam-plate engaging said pistons and elfecting their reciprocation in said bores as said rotor is rotated, the other of said end faces of said rotor having therein a plurality of ports communicating one with each said bore; a stationary thrust face in said housing coacting with said other end face of the rotor and having therein an arcuate inlet aperture and a pair of circumferentially-spaced outlet apertures coaxial with the axis of said rotor, a bearing mounting for said camplate, whereby it is adjustable circumferentially to vary the angular positions of the beginning and end of the suction and discharge strokes of said pistons with respect to said inlet and outlet apertures and thereby to alter the effective arcuate length of said apertures, and means, operable to effect the angular adjustment of said camplate in response to change of altitude at which the pump is operated, said cam-plate adjusting-means including an evacuated capsule, arranged to produce a signal dependent upon an absolute pressure derived from atmospheric pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,561,519 7/51 Leech 130-37 2,875,743 3/59 Druzynski. 3,160,104 12/64 Barnard 103-162 X DONLEY J. STOCKING, Primary Examiner. LAURENCE V. EFNER, Examiner. 

1. A LIQUID PUMP COMPRISING A HOUSING, A ROTOR MOUNTED WITHIN A SAID HOUSING AND HAVING A PAIR OF OPPOSED END FACES AND A PLURALITY OF BORES THEREIN EXTENDING BETWEEN SAID END FACES; A PISTON IN EACH BORE; A SPRING IN EACH BORE OPERABLE TO BIAS THE RESPECTIVE PISTON TOWARDS A POSITION IN WHICH IT EXTENDS FROM ONE OF SAID END FACES; A CAM-PLATE COAXIAL WITH, BUT INCLINED TO, THE AXIS OF ROTATION OF SAID ROTOR AND POSITIONED ADJACENT SAID ONE END FACE OF SAID ROTOR, SAID CAM-PLATE ENGAGING SAID PISTONS AND EFFECTING THEIR RECIPROCATION IN SAID BORES AS SAID ROTOR IS ROTATED, THE OTHER OF SAID END FACES OF SAID ROTOR HAVING THEREIN A PLURALITY OF PORTS COMMUNICATING ONE WITH EACH SAID BORE; A STATIONARY THRUST FACE IN SAID HOUSING COACTING WITH SAID OTHER END FACE OF THE ROTOR AND HAVING THEREIN ARCUATE INLET AND OUTLET APERTURES COAXIAL WITH THE AXIS OF SAID ROTOR, A BEARING MOUNTING FOR SAID CAM-PLATE, WHEREBY IT IS ADJUSTABLE CIRCUMFERENTIALLY TO VARY THE ANGULAR POSITIONS OF THE BEGINING AND END OF THE SUCTION AND DISCHARGE STROKES OF SAID PISTONS WITH RESPECT TO SAID ARCUATE INLET AND OUTLET APERTURES AND THEREBY TO ALTER THE EFFECTIVE ARCUATE LENGTH OF SAID APERTURES, AND MEANS, OPERABLE TO EFFECT THE ANGULAR ADJUSTMENT OF SAID CAM-PLATE IN RESPONSE TO CHANGE OF ALTITUDE AT WHICH THE PUMP IS OPERATED, SAID CAM-PLATE ADJUSTING MEANS INCLUDING AN EVACUATED CAPSULE, ARRANGED TO PRODUCE A SIGNAL DEPENDENT UPON AN ABSOLUTE PRESSURE DERIVED FROM ATMOSPHERIC PRESSURE. 